1. Field of the Invention
The invention relates to a circuit for converting AC voltage into a non-stabilized DC voltage for at least one device, the circuit comprising:
an AC voltage supply,
a rectifier module having two inputs connected to the AC voltage supply and outputs connected to two output lines with external terminals for coupling at least one device; and
at least one induction coil arranged between the AC voltage supply and the rectifier module.
2. Description of the Related Art
A multiplicity of electrical or electronic devices require a DC voltage for their operation, this DC voltage having to be provided or generated from the AC voltage supplied by the power supply system. Representative of such devices are television sets (TV). The circuits for conversion of the AC voltage into DC voltage used in these devices must meet certain requirements concerning their conversion behavior, in particular, in respect of the residual system harmonics content. Such requirements are the subject of standards, of which, particularly, EN 61000-3-2 can be named, which, with effect from 2001, must be complied with in Europe by terminals that have a power input of more than 75 W.
In order to ensure the said quality standards are met, there are a number of different possibilities with varying optimum performance ranges. For high powers, from approximately 500 W upwards, active solutions predominate. In the lower power range, on the other hand, 50 Hz coils are often to be found. They are relatively cheap, but also relatively large and heavy. This size or this concentration of weight leads to problems with the available space on printed circuit boards, or to problems with the impact resistance of the equipment manufactured.
Against this background, the object of the present invention is to provide a circuit for conversion of AC voltage into a DC voltage for at least one consumer, which guarantees sufficient quality of the conversion behavior with limited space and cost requirements.
This object is achieved in a circuit for converting an AC voltage into a DC voltage for at least one device, comprising:
(a) An AC voltage supply for providing the AC voltage for conversion;
(b) A rectifier module having two inputs connected to the AC voltage supply for receiving the AC voltage, and two DC voltage outputs from which corresponding output lines lead with external terminals are connectable to at least one device;
(c) A main capacitor connected in parallel to a device to be connected between the two external terminals the rectifier module; and
(d) At least one induction coil arranged in one of the lines connecting the AC voltage supply to the rectifier module, the induction coil smoothing a recharging current or reducing a harmonic content of the recharging current,
characterized in that the circuit also comprises:
(e) A further capacitor connected in parallel to the main capacitor between the two outputs of the rectifier module;
(f) At least one diode connected in one of the output lines of the rectifier module, said at least one diode separating the main capacitor from the further capacitor, and being forward-biased relative to the DC voltage output of the rectifier module; and
(g) An active converter having an input connected between the diode and the rectifier module (and thus to a plate of the further capacitor), and arranged to discharge the further capacitor at least in part in the second half of each half-wave supplied by the AC voltage supply.
The behavior of the input current is altered in an advantageous manner through the further capacitor, which can have a relatively small capacitance, and through the discharge process via the active converter. There is particularly a reduction in the harmonic part. This can, in turn be, used for designing the induction coil to be correspondingly smaller, because the required inductance L can be selected to be smaller. In this way, it is possible to use inductor coils with a drastically reduced size, which can be used when space is limited on printed circuit boards, and to avoid problems with the impact resistance of the devices. Compliance with the relevant standards is also guaranteed.
The active converter may be an up-controller or up-converter. The energy transported by the converter may either be fed to the main capacitor to supply power to the switched-mode regulator ICs of a downstream DCxe2x80x94DC converter or directly to a load on the line voltage-isolated side (secondary side) of a downstream DCxe2x80x94DC converter.